Kinetic analysis of the cyclic cascade model reveals that, in addition to the advantages described before, the cyclic cascade can function as a rate amplifier, and since the steady-state can be established in the millisecond range, it is suitable for most biological processes which require signal amplification such as neural transmission and hormonal control. The study of the adenylylation and deadenylylation of glutamine synthethase confirmed some of the basic properties revealed by the cyclic cascade model. (2) Elucidation of the catalytic cycle for alkaline phosphatase shows that a flip-flop mechanism is inappropriate for explaining the observed negative cooperativity. The study of feedback inhibitors revealed the existence of allosteric sites and the points in the glutamine synthetase catalytic cycle at which the inhibitors act. The former was confirmed by the NMR and fluorescence studies on inhibitor binding. (3) Distance determinations by NMR, ESR and fluorescence energy transfer methods reveal the close distance between the covalent regulatory site and the catalytic site on glutamine synthetase. Other studies included binding of methionine sulfoximine, thyroxine transport proteins, carcinogen N-hydroxy-N-acetyl-2-amino-fluorene and blood clotting system.